Tip of the Day 164: Piezo Sensors Do Not Detect Disconnects

It’s all in the title.

Some of our customers have thought that because our Lynx Piezo sensors have the integrated case electronics that they would behave the same as the strain gage sensors in detecting disconnections or broken wires. This is not true. When a piezo sensor becomes disconnected or its wire cut it simply reads zero pressure. Here is why.

A piezo sensor is made with a crystal sandwiched between two wires. It puts out charge (electrons) in one direction or the other during change in pressure. When the pressure is not changing it just sits there, inert and doing nothing.

The crystal itself is a superb electrical insulator. The schematic symbol looks like this:

The crystal, when not being pressurized or depressurized, looks exactly like air. Disconnecting the wire like this…

…appears to the Lynx electronics just the same as the sensor when connected. Thus if you disconnect a piezo sensor or do not connect the cable from the piezo adapter to the sensor then the electronics sees no change and reports zero pressure.

The strain gage sensors, on the other hand, will drive the electronics to the limit when a wire is cut, shorted or broken. This is how the strain gage electronics can detect that kind of damage and report to the eDART that the sensor reading is not good.